In a previous study (Simonson 1975, ApJ, 201, L103), the H I
feature at l = 197, b = +2, with radial velocities extending
from v = –30 to –87 km/s, has been attributed to a low-mass
galaxy being tidally disrupted as it approaches the Milky
Way. Although several local hypotheses have been advanced to
explain the H I feature, quantitative support has been
lacking for the energy requirements to account for the wide
velocity range observed. On the other hand, the rotation of
a gaseous disk in an external galaxy naturally displays such
a velocity range. A simple dynamical model accounts for the
velocity pattern not only of this feature but also of the
stream of high-velocity H I clouds starting at this location
and extending to l = 155, b = +8, crossing l = 180 at v =
–90 km/s. In this tidal disruption model, calculations show
that the distance to the approaching galaxy is directly
related to the mass of the Milky Way. Given a current
estimate of about 1.2e12 suns, the mass of the small galaxy
is in the range 6-10e8 suns (mostly dark matter), and the
distance modulus is about m – M = 20 mag. For a range of
Milky Way mass estimates, plus uncertainties in matching the
model to the observations, m – M could range from 19 to 21.5
mag. The absorption in the visual is estimated to be 3 – 4
mag. The lack of optical counterparts detected until now
implies a Low Surface Brightness dwarf galaxy. It may
currently be feasible to detect the stellar component of the
inferred galaxy, using techniques similar to those employed
in the case of the Sagittarius dwarf galaxy and tidal
streams in the halo of the Milky Way. (Work performed under
the auspices of the U.S. Department of Energy by the
Lawrence Livermore National Laboratory under contract No.
W-7405-ENG-48.)